Optimization of hydrogen production from steam reforming of biomass tar over Ni/dolomite/La2O3 catalysts

Industrially, the endothermic process of steam reforming is carried out at the lowest temperature, steam to carbon (S/C) ratio, and gas hourly space velocity (GHSV) for maximum hydrogen (H₂) production. In this study, a three-level three factorial Box-Behnken Design (BBD) of Response Surface Methodology (RSM) was applied to investigate the optimization of H₂ production from steam reforming of gasified biomass tar over Ni/dolomite/La₂O₃ (NiDLa) catalysts. Consequently, reduced quadratic regression models were developed to fit the experimental data adequately. The effects of the independent variables (temperature, S/C ratio, and GHSV) on the responses (carbon conversion to gas and H₂ yield) were examined. The results indicated that reaction temperature was the most significant factor affecting both responses. Ultimately, the optimum conditions predicted by RSM were 775 °C, S/C molar ratio of 1.02, and GHSV of 14,648 h⁻¹, resulting in 99 mol% of carbon conversion to gas and 82 mol% of H₂ yield.     

Modelling of H2 production via sorption enhanced steam methane reforming at reduced pressures for small scale applications

The production of H₂ via sorption enhanced steam reforming (SE-SMR) of CH₄ using 18 wt % Ni/Al₂O₃ catalyst and CaO as a CO₂-sorbent was simulated for an adiabatic packed bed reactor at the reduced pressures typical of small and medium scale gas producers and H₂ end users. To investigate the behaviour of reactor model along the axial direction, the mass, energy and momentum balance equations were incorporated in the gPROMS modelbuilder^®. The effect of operating conditions such as temperature, pressure, steam to carbon ration (S/C) and gas mass flow velocity (G_s) was studied under the low-pressure conditions (2–7 bar). Independent equilibrium based software, chemical equilibrium with application (CEA), was used to compare the simulation results with the equilibrium data. A good agreement was obtained in terms of CH₄ conversion, H₂ yield (wt. % of CH₄ feed), purity of H₂ and CO₂ capture for the lowest (G_s) representing conditions close to equilibrium under a range of operating temperatures pressures, feed steam to carbon ratio. At G_s of 3.5 kg m⁻²s⁻¹, 3 bar, 923 K and S/C of 3, CH₄ conversion and H₂ purity were up to 89% and 86% respectively compared to 44% and 63% in the conventional reforming process.     

Integrated catalytic adsorption (ICA) steam gasification system for enhanced hydrogen production using palm kernel shell

This paper investigates the integrated catalytic adsorption (ICA) steam gasification of palm kernel shell for hydrogen rich gas production using pilot scale fluidized bed gasifier under atmospheric condition. The effect of temperature (600–750 °C) and steam to biomass ratio (1.5–2.5 wt/wt) on hydrogen (H₂) yield, product gas composition, gas yield, char yield, gasification and carbon conversion efficiency, and lower heating values are studied. The results show that H₂ hydrogen composition of 82.11 vol% is achieved at temperature of 675 °C, and negligible carbon dioxide (CO₂) composition is observed at 600 °C and 675 °C at a constant steam to biomass ratio of 2.0 wt/wt. In addition, maximum H₂ yield of 150 g/kg biomass is observed at 750 °C and at steam to biomass ratio of 2.0 wt/wt. A good heating value of product gas which is 14.37 MJ/Nm³ is obtained at 600 °C and steam to biomass ratio of 2.0 wt/wt. Temperature and steam to biomass ratio both enhanced H₂ yield but temperature is the most influential factor. Utilization of adsorbent and catalyst produced higher H₂ composition, yield and gas heating values as demonstrated by biomass catalytic steam gasification and steam gasification with in situ CO₂ adsorbent.     

Optimal design of parallel channel patterns in a micro methanol steam reformer

This study describes the performance of micro methanol steam reformers with channel widths optimized using the simplified conjugate gradient method (SCGM), which uses a minimum objective function of the H₂ mass fraction standard deviation in channels. A three-dimensional numerical model and optimal simplified conjugate gradient algorithm were built to predict and search for the effects of channel widths and flow rate on the performance of chemical reactions. Furthermore, this simulation model was compared to; and corresponded well with existing experimental data. Distributions of velocity, temperature, and gas concentrations (CH₃OH, CO, H₂, and CO₂) were predicted, and the methanol conversion ratio was also evaluated. The mole fraction of CO contained in the reformed gas, which is essential to preventing poisoning of the catalyst layers of fuel cells, is also investigated. In the optimization search process, the governing equations use the continuity, momentum, heat transfer, and species equations to evaluate the performance of the steam reformer. The results show that channel width optimization can not only increase the methanol conversion ratio and hydrogen production rate but also decrease the concentration of carbon monoxide. The velocity and mixture gas density distributions in channels are discussed and plotted at various locations for an inlet liquid flow rate of 0.3 cc min⁻¹. Full development is not obtained in the downstream channel flow, the velocity in channel is increased from 1.28 m s⁻¹ to 2.36 m s⁻¹ at location Y = 1 mm–32 mm, respectively. This can be attributed to a continuous increase in the lightweight H₂ species as a result of chemical reactions in the channels.     

Enhanced hydrogen production via staged catalytic gasification of rice husk using Ca(OH)2 adsorbent and Ce–Ni/γAl2O3 catalyst in a fluidized bed

Hydrogen production from rice husk was carried out via a two-stage system combining CLG (calcium looping gasification) using Ca(OH)₂ adsorbent in a bubbling fluidized bed and catalytic reforming with Ce–Ni/γAl₂O₃ catalyst in a connected fixed bed. The results show that the maximum H₂ concentration (69.16 vol%) and H₂ yield (11.86 mmol g⁻¹rice husk) are achieved at Ca/C (Ca(OH)₂ to carbon molar ratio) = 1.5, H₂O/C (H₂O to carbon molar ratio) = 1.5, T_g (gasification temperature) = 500 °C, T_c (catalytic temperature) = 800 °C. The supplementation of fresh Ca(OH)₂ at Ca/C of 0.5 during calcination helps to activate the regenerated CaO by hydration, maintaining its carbonation activity and CO₂ adsorption. Ce–Ni/γAl₂O₃ catalyst promotes water gas shift (WGS), steam methane reforming (SMR), and C₂–C₃ hydrocarbons reforming, also exhibits excellent activity stability to maintain H₂ concentration and H₂ yield above 67.21 vol% and 11.67 mmol g⁻¹_{rice husk}, respectively, during 5 lifetime tests.     

An experimental investigation of hydrogen production from biomass gasification

An experimental study of hydrogen production from biomass was conducted using a benchscale fluidized bed gasifier. Parametric experiments were performed to determine the effects of reactor temperature, equivalence ratio, and steam to biomass ratio. Experimental measurements of gas composition and yield were used to calculate the hydrogen yield potential, the capacity of the gas stream for hydrogen production by shifting carbon monoxide and steam reforming higher hydrocarbons. Over the ranges of experimental conditions examined, hydrogen yield potential proved to be most sensitive to equivalence ratio, varying from 62 g H₂ kg⁻¹ of dry, ash-free biomass at an equivalence ratio of 0.37, to 128 g H₂ kg⁻¹ of dry, ash-free biomass at an equivalence ratio of 0.0. Of the conditions tested, the highest hydrogen yield potential, 128 g H₂ kg⁻¹ of dry, ash-free biomass, was achieved at a reactor temperature of 850 °C, equivalence ratio of 0.0, and a steam to biomass ratio of 1.7. This is 78% of the theoretical maximum yield of 165 g H₂ kg⁻¹ of dry, ash-free biomass for this feedstock.     

Hydrogen production from steam gasification of tableted biomass in molten eutectic carbonates

The steam gasification of tableted biomass for H₂ production in molten salts was investigated under different conditions. The results showed that the ternary molten carbonates (32 wt% Li₂CO₃, 33 wt% Na₂CO₃ and 35 wt% K₂CO₃) acted as heat medium and catalyst in the gasification process. The use of molten salts could significantly increase total gas and H₂ production and simultaneously decrease the concentrations of CO and CH₄ in the product gas, and also decrease the yield of condensable tar. The increase in gasification temperature and mass ratio of steam to biomass (S/B) was beneficial for H₂ production process. However, excessive steam contributed slightly to the increase in H₂ production and largely increased the energy consumption. The optimal S/B ratio was found to be 1.0. The feedstock after tabletting could completely immersed in molten salts, which improved the contact between biomass and molten salts and thus favored the biomass gasification for H₂ production. When biomass particle size was 0.25 g/piece, the yield of H₂ reached 807.53 mL/g biomass.     

Alkaline pyrolysis of anaerobic digestion residue with selective hydrogen production

Hydrogen (H₂) production from biomass has attracted the research attention as it is renewable and clean. This work investigates the alkaline pyrolysis (AP) of corn stover digestate (CSD) with sodium hydroxide (NaOH) to promote the production of H₂ and suppress carbon dioxide (CO₂) at moderate conditions. It is observed that the H₂ production is affected by the mass ratio of CSD to NaOH and reaction temperature. The H₂ yield is enhanced from 1:1 to 1:2 ratio of CSD to NaOH (10.9–25.9 mmol g⁻¹) with the purity of 81.21–84.98% at 500 °C, whereas a slight increase in H₂ production at 1:3 ratio of CSD to NaOH is observed which may attribute to the mass transfer matter. The possible mechanism of AP is identified. Through the thermogravimetric analysis (TGA), distributed activation energy model (DAEM) was applied which evidences the catalytic ability of NaOH via the reduced activation energies.     

Development of a H2-permeable Pd60Cu40-based composite membrane using a reverse build-up method

A new reverse build-up method is developed to fabricate an economical H₂-permeable composite membrane. Sputtering and electroplating are used for the formation of a membrane comprised of a 3.7-μm-thick Pd₆₀Cu₄₀ (wt.%) alloy layer and a 13-μm-thick porous Ni support layer, respectively. The H₂-permeation measurements are performed under the flow of a gaseous mixture of H₂ and He at 300–320 °C and 50–100 kPa of H₂ partial pressure. The H₂/He selectivity values exceed 300. The activation energy at 300–320 °C is 10.9 kJ mol⁻¹. The H₂ permeability of the membrane is 1.25 × 10⁻⁸ mol m⁻¹ s⁻¹ Pa^−0.5 at 320 °C after 448 h. The estimated Pd cost of the proposed membrane is approximately 1/8 of the cost for a pure Pd₆₀Cu₄₀ membrane. This study demonstrates that the proposed method allows the facile production of low-cost, Pd-based membranes for H₂ separation.     

Agglomerated Co–Cr/SBA-15 catalysts for hydrogen production through acetic acid steam reforming

Hydrogen produced from renewable resources is becoming interesting as an alternative to conventional fossil fuels. Co-based catalysts have been reported for their active role in steam reforming of acetic acid as the main model compound of bio-oil aqueous fraction. In the present work, a series of Co–Cr/SBA-15 extrudates were prepared by varying the binder (bentonite) content and particle size in order to get catalyst particles suitable to be used in a steam reformer at industrial scale. Catalysts were characterized by N₂ physisorption, ICP-AES, TEM, SEM, XRD and H₂-TPR. The physicochemical characterization results showed that no remarkable changes occurs after the extruding process of the powdered sample, except for the particle size and mechanical strength. Acetic acid steam reforming tests were done at 600 °C and WHSV = 30.1 h⁻¹ varying the feed flow rate and the catalysts particle size in order to study the influence of internal and external diffusion limitations. Extruded particles with an effective diameter of 1.5 mm and 30 wt% of bentonite get similar conversion and hydrogen selectivity than powder sample. Besides, the agglomerated catalysts are also stable up to 12 h of TOS.     

Experimental investigation of the effect of physical pre-treatment on air-blown fluidized bed biomass gasification

The effect of comminution, drying, and densification on bubbling fluidized bed gasification was investigated by fractionating a forestry residue into a feedstock consisting of different particle sizes, moisture levels, and by densifying to pellets. The gasification performance was evaluated at nominal average bed temperatures of 725°, 800° and 875 °C at a constant fluidizing velocity (0.91 m s⁻¹) with feed input rates between 9 and 24 kg h⁻¹.The gas composition was observed to be influenced by both the particle size and form. Smaller particles led to a gas richer in carbon monoxide and depleted in hydrogen. The gasification of pellets led to a gas with the greatest hydrogen to carbon monoxide ratio. The smallest particles tested resulted in the worst gasification performance, as defined by cold gas efficiency, carbon conversion, and tar production. Despite differences in the gas composition among the larger particles and the pellets, similar carbon conversion and cold gas efficiency was observed.Relative to comparable test conditions with dry feed fractions (having a moisture mass fraction of 7–12%), an average 11% increase in carbon conversion was observed for the wetter feed fractions containing a moisture mass fraction of 24–31%. This increase in carbon conversion offset much of the expected decrease in cold gas efficiency by using a wetter feed material. A slight increase in hydrogen production and negligible change in tar production was observed for the wetter feed fractions relative to the dry feed fraction.     

Turning glycerol surplus into renewable syngas through glycerol steam reforming over a sol-gel Ni–Mo2C-Al2O3 catalyst

In this work, a sol-gel Ni–Mo₂C–Al₂O₃ catalyst is employed for the first time in the glycerol steam reforming for syngas production. Catalyst stability and activity are investigated in the temperature range of 550 °C–700 °C and time on stream up to 30 h. As reaction temperature increases, from 550 °C to 700 °C, H₂ yield boosts from 22% to 60%. The stability test, carried out at milder conditions (600 °C and Gas-Hourly Space-Velocity (GHSV) of 50,000 mL h⁻¹.g_cat⁻¹), shows high catalyst stability, up to 30 h, with final conversion, H₂ yield, and H₂/CO ratio of 95%, 53% and 1.95, respectively. Both virgin and spent catalysts have been characterized by a multitude of techniques, e.g., Atomic-Absorption spectroscopy, Raman spectroscopy, N₂-adsorption-desorption, and Transmission Electron Microscopy (TEM), among others. Regarding the spent catalysts, carbon deposits’ morphology becomes more graphitic as the reaction temperature increases, and the total coke formation is mitigated by increasing reaction temperature and lowering GHSV.     

Methanol steam reforming over highly efficient CuO–Al2O3 nanocatalysts synthesized by the solid-state mechanochemical method

CH₃OH steam reforming is an attractive way to produce hydrogen with high efficiency. In this study, CuO.xAl₂O₃ (x = 1, 2, 3, and 4) were fabricated based on the solid-state route, and the calcined samples were employed in methanol steam reforming at atmospheric pressure and in the temperature range of 200–450 °C. The results revealed that all samples have a high BET area (173–275 m² g⁻¹), and their crystallinity was reduced by increasing the alumina content in the catalyst formulation. The catalytic activity tests showed that the CH₃OH conversion and H₂ selectivity decreased by rising the Al₂O₃·CuO molar ratio. The methanol conversion enhanced from 13% to 85% by increasing the reaction temperature from 200 °C to 450 °C over the CuO·Al₂O₃ catalyst, due to the higher reducibility of this catalyst at lower temperatures compared to other prepared samples. The influence of calcination temperature (300–500 °C), GHSV (28,000–48000 ml h⁻¹. g⁻¹_cat), feed ratio (C:W = 1:1 to 1:9), and reduction temperature (250–450 °C) was also determined on the yield of the chosen sample. The results revealed that the maximum methanol conversion decreased from 90 to 79% by raising the calcination temperature from 300 to 500 °C due to the reduction of surface area and sintering of species at high calcination temperatures.     

An investigation into the effect of fast heating on fluidity development and coke quality for blends of coal and biomass

The addition of biomass to coking coals can reduce operational costs and carbon emissions but also reduces fluidity development. The use of heating rates up to 20 °C min⁻¹ in the softening stage of coal has been investigated using high-temperature small-amplitude oscillatory-shear (SAOS) rheometry to improve the fluid characteristics of binary blends of two coking coals with Scots pine. The effects of biomass concentration and particle size, biomass torrefaction, pellet mass and thermal pre-treatment of the blend on fluidity development and semicoke strength have also been studied. Fluidity increased with an increase in heating rate and an increase in the final temperature for fast heating. Relationships were found between the minimum complex viscosity of the blend, the heating rate and the concentration of biomass, which have been used to propose an equation to calculate the heating rate necessary to achieve optimum fluidity for a particular blend with biomass. The fluid characteristics of the blend were not affected to a great extent by the particle sizes of the biomass studied (<500 μm and >500 μm) or the torrefaction of the biomass (250 °C for 1 h in N₂), were increased by an increase in pellet mass, and were destroyed by blend pre-heating. The semicoke strength of the blend with a mass fraction of 10% Scots pine and fast heating (10 °C min⁻¹) proved to be higher than that of the coal alone with slow heating (3 °C min⁻¹) and resulted in a 3% reduction in non-renewable carbon emissions.     

Controlling the rate of change of Ni dispersion in commercial catalyst by ALD overcoat during dry reforming of methane

This study investigates changes in dispersion with time-on-stream of a Ni catalyst coated with alumina by Atomic Layer Deposition (ALD) in Dry Reforming of Methane (DRM) conditions. A 20 wt% commercial Ni catalyst is coated with 5, 10, and 20 ALD cycles and tested for DRM at 650 °C, 1 atm for 40 h. Using an in-situ H₂–CO pulse chemisorption technique, it is found that the rate of decline in catalyst dispersion is more rapid in the uncoated catalyst (~0.11%h⁻¹) than 5-ALD catalyst (~0.025%h⁻¹). TEM images before and after reaction show that the average particle size for the uncoated catalyst increases from 8.5 nm to 24.5 nm, indicating sintering, whereas the 5-ALD catalyst retained the initial particle size. The reduced particle size also explains the 50% reduction in carbon formation-rate in the 5-ALD catalyst. The developed sequential H₂–CO chemisorption technique reliably measures in-situ dispersion in uncoated and ALD coated catalysts with exposed active sites.     

Steam reforming of methanol for ultra-pure H2 production in a membrane reactor: Techno-economic analysis

Process simulation and design as well as economic analysis were carried out to evaluate technical and economic feasibility of steam reforming of methanol in a membrane reactor (MR) for ultra-pure H₂ production. Using a commercial process simulator, Aspen HYSYS®, comparative studies were conducted to investigate the effect of operating conditions including the H₂ permeance (1 × 10⁻⁵ - 6 × 10⁻⁵ mol m⁻² s⁻¹ Pa⁻¹), a H₂O sweep gas flow rate (1–20 kmol h⁻¹), and a reaction temperature (448–493 K) in a conventional packed-bed reactor (PBR) and the MR using a previously reported reaction kinetics. Improved performances such as methanol conversions and H₂ yields were observed in the MR compared to the PBR and several design guidelines for the MR were obtained to develop H₂ separation membranes with optimal H₂ permeance and to select a suitable H₂O sweep gas flow rate. In addition, economic analysis based on itemized cost estimations was conducted for a small-sized H₂ fueling station by calculating a unit H₂ production cost for both the PBR and the MR reflecting a current economic status in Korea. As a result, a cost saving of about 23% was obtained in the MR (7.24 $ kgH₂⁻¹) compared to the PBR (9.37 $ kgH₂⁻¹) confirming the benefit of employing the MR for ultra-pure H₂ production.     

Gasification of torrefied oil palm biomass in a fixed-bed reactor: Effects of gasifying agents on product characteristics

Gasification represents an attractive pathway to generate fuel gas (i.e., syngas (H₂ and CO) and hydrocarbons) from oil palm biomass in Malaysia. Torrefaction is introduced here to enhance the oil palm biomass properties prior to gasification. In this work, the effect of torrefaction on the gasification of three oil palm biomass, i.e., empty fruit bunches (EFB), mesocarp fibres (MF), and palm kernel shells (PKS) are evaluated. Two gasifying agents were used, i.e., CO₂ and steam. The syngas lower heating values (LHV_syngas) for CO₂ gasification and steam gasification were in the range of 0.35–1.67 MJ m⁻³ and 1.61–2.22 MJ m⁻³, respectively. Compared with EFB and MF, PKS is more effective for fuel gas production as indicated by the more dominant emission of light hydrocarbons (CH₄, C₂H₄, and C₂H₆) in PKS case. Gasification efficiency was examined using carbon conversion efficiency (CCE) and cold gas efficiency (CGE). CCE ranges between 4% and 55.1% for CO₂ gasification while CGE varies between 4.8% and 46.2% and 27.6% and 62.9% for CO₂ gasification and steam gasification, respectively. Our results showed that higher concentration of gasifying agent promotes higher carbon conversion and that steam gasification provides higher thermal efficiency (CGE) compared to CO₂ gasification.     

Explosion characteristics of pulverised torrefied and raw Norway spruce (Picea abies) and Southern pine (Pinus palustris) in comparison to bituminous coal

Pre-treatments, such as torrefaction, can improve biomass fuels properties. Dedicated and coal co-firing plants, in which pulverised biomass and torrefied biomass can be used, are exposed to explosion hazards during handling, storage and transport from the mills to the boiler. Data on the explosion characteristics of biomass and torrefied biomass are scarce. This study presents explosion characteristics (maximum explosion pressure, deflagration index and minimum explosible concentration) of two torrefied wood samples and compares their reactivity to that of their corresponding untreated biomass materials and to a sample of Kellingley coal. Torrefied biomass samples showed higher reactivity, overpressures were around 9 bar (0.9 MPa, 1 bar = 10⁵ Pa) for all biomass samples irrespective of size or sample composition. Derived laminar burning velocities ranged between 0.1–0.12 m s⁻¹, and were therefore similar to that of coal (0.12 m s⁻¹). The differences in explosion reactivity influence the design of explosion protection measures and can be used to introduce suitable modifications for safe operations with torrefied biomass.     

Application of an empirical model in CFD simulations to predict the local high temperature corrosion potential in biomass fired boilers

To gain reliable data for the development of an empirical model for the prediction of the local high temperature corrosion potential in biomass fired boilers, online corrosion probe measurements have been carried out. The measurements have been performed in a specially designed fixed bed/drop tube reactor in order to simulate a superheater boiler tube under well-controlled conditions. The investigated boiler steel 13CrMo4-5 is commonly used as steel for superheater tube bundles in biomass fired boilers. Within the test runs the flue gas temperature at the corrosion probe has been varied between 625 °C and 880 °C, while the steel temperature has been varied between 450 °C and 550 °C to simulate typical current and future live steam temperatures of biomass fired steam boilers. To investigate the dependence on the flue gas velocity, variations from 2 m·s⁻¹ to 8 m·s⁻¹ have been considered. The empirical model developed fits the measured data sufficiently well. Therefore, the model has been applied within a Computational Fluid Dynamics (CFD) simulation of flue gas flow and heat transfer to estimate the local corrosion potential of a wood chips fired 38 MW steam boiler. Additionally to the actual state analysis two further simulations have been carried out to investigate the influence of enhanced steam temperatures and a change of the flow direction of the final superheater tube bundle from parallel to counter-flow on the local corrosion potential.     

Enhanced hydrogen production by the catalytic alkaline thermal gasification of cellulose with Ni/Fe dual-functional CaO based catalysts

A two-stage system involving alkaline thermal gasification of cellulose with Ca(OH)₂ sorbent and catalytic reforming with Ni/Fe dual-functional CaO based catalysts is proposed and applied to enhance H₂ production and in-situ CO₂ capture. The results show that the H₂ concentration is maximized at a considerably lower temperature (500 °C) than commercialized biomass gasification processes, reducing energy consumption. Sol-gel method is deemed better than impregnation method for its lower cost and higher-concentration H₂ production. Among the prepared catalysts, sol-NiCa catalyst exhibits the best performance in CO₂ absorption, resistance to carbon deposition, and cyclic stability, creating maximum H₂ concentration (79.22 vol%), H₂ yield (27.36 mmol g⁻¹ cellulose), and H₂ conversion (57.61%). Introduction of Ni rather than Fe on the CaO based catalyst promotes steam methane reforming at moderate temperature range of 400–600 °C, generating low contents of CH₄ (5.38 vol%), CO₂ (4.82 vol%), and CO (10.58 vol%).